Ozone, chemically recognized as having three oxygen atoms per molecule, exists in the atmosphere as an unstable blue gas with a very characteristic odor that is easy to recognize. At levels below about 0.005 parts per million (ppm), ozone makes the air smell fresh and in concentrations of about 10 to about 20 ppm at higher altitudes, its color makes the sky blue. At altitudes from about 4 to about 6 miles above the earth, ozone is created from oxygen irradiated by a portion of the sun's ultraviolet spectrum and functions as a powerful absorber of harmful ultraviolet rays.
At ground level, ozone exists in a greatly diluted state and is always present in minute quantities of approximately 0.001 ppm to approximately 0.003 ppm, which we breathe in. It does not become an irritant until levels above about 0.1 ppm are exceeded for over about eight hours. Below those levels, there have not been any reports of permanent detrimental effects from inhaling it.
Ozone is created naturally, at ground level, by crashing surf, whitewater rapids, waterfalls and lightning storms. Ozone was discovered in 1840; the first ozone generators were developed by Werner von Siemens in 1857. For about 150 years, man has been able to generate ozone and has been relentless in finding ways to use ozone beneficially.
The first medical use of ozone was in 1870 to purify blood in test tubes. Other medical uses followed but not without controversy. Ozone has long been recognized as a very powerful oxidant and is used in over thirty different industries as an industrial oxidizer and sterilizer. Examples of some existing applications include, but are not limited to, manufacture of synthetic fibers, chemicals, jet lubricants, air scrubbing for clean rooms, treatment of industrial wastes, potable water treatment, bottling plants, sewage treatment, aquaculture, aquarium sanitation, food preservation, sterilization of containers, deodorization, pulpwood bleaching, and metal extraction.
While ozone is very powerful, it has a very short life span of approximately 20 minutes at ambient conditions. After completing its job, it reverts back to oxygen, as explained below. This means that ozone is usually produced on site. When in an area with contaminants such as odors, bacteria, or viruses, the extra atom of oxygen destroys them completely by oxidation. Ozone's most well known use is in water treatment as a primary stage disinfectant because of its bactericidal and virucidal efficacy. Different uses of ozone require different concentrations to obtain desired results.
Ozone generators have been widely used in the past decade for production of ozone as an indoor air cleansing agent. Machines that purposefully produce ozone are currently on the market for residential use. Above certain concentrations, ozone is a potent lung irritant that can cause respiratory distress, and levels of ozone that clean air effectively are unsafe to human health. Thus, in State of Alaska Epidemiology Bulletin No. 36, dated Sep. 8, 1997, “Ozone Generators—Warning—Not for Occupied Spaces,” the Alaska Division of Public Health warns Alaskans not to use ozone generating devices in occupied spaces such as vehicles or residential homes.
The U.S. Food and Drug Administration prohibits devices that result in more than 0.050 ppm of ozone in the air of occupied enclosed spaces such as homes, offices, or vehicles, or that result in any releases of ozone in places occupied by the ill or infirm. The elderly, families with children, and people with respiratory diseases such as asthma are the most susceptible to the toxic effects of ozone, and are ironically among those most likely to be benefit from having cleaner indoor air.
Thus, there is a very delicate balancing act for providing ozone generators for indoor air cleansing at levels not considered harmful to desirable indoor life—plants, animals, and people. U.S. Pat. No. 5,681,533 to Hiromi describes an environment decontaminating system with an air cleaning and deodorizing function that controls the ozone concentration such that it remains lower than 0.06 ppm. U.S. Pat. No. 6,363,951 to Wood discloses an ozonation system that diffuses ozone into water used to wash foods, plates, utensils and the like, while a venting system or carbon filter is used to eliminate or destroy any ozone that escapes the water bath. Similarly, U.S. Pat. No. 6,872,366 describes a specially constructed chamber for ozone generation for disinfection of hands and forearms of health care providers. The exhaust outlet holes are covered by a fabric, such as wool, to neutralize ozone before it can escape to the environment surrounding the generator.
U.S. Pat. No. 6,589,486 to Spanton discloses an air purifying apparatus and method that is located in a forced air heating, ventilating, and air conditioning system that uses ultraviolet (UV) radiation to kill bacteria and viruses and ozone at a “safe and balanced” concentration of 0.2 to 0.3 ppm to destroy organisms not killed by the UV radiation.
There is also a contrary view of the use of ozone to clean indoor air in U.S. Pat. No. 6,494,934 to Fukushima describing a quick air cleaning and air sterilization system that avoids use of ozone because ozone is considered harmful and uncomfortable for persons.
There is a continuing need for effective ozone generators.